174 BRITISH TYROGLYPHJDJE. 



DEVELOPMENT or THE REPRODUCTIVE ORGANS. 



Nalepa investigated this with his usual care in 

 Carpoglyphits anonymus, and wrote an excellent account 

 of it, which I will give an abstract of here.* He says 

 that the idea is widely spread that the larvae and 

 nymphs of Acari do not show any signs which would 

 enable anyone to distinguish sex, but this is based only 

 upon the external characters. A study of the internal 

 organs shows that only the larvse and first nymph (i. e. 

 the nymph after the larval, but before the first nymphal 

 ecdysis) are sexually indifferent ; the second nymph 

 shows differences (in G. anonymus). The whole of the 

 following account is Nalepa' s, not mine. 



The first indication of the generative gland is 

 between the proctodeum and the posterior end of the 

 ventral plate ; it consists of two rounded cell-masses, 

 the formation of which from the blastoderm Nalepa 

 was not able to trace, but which he suggests were 

 probably of epiblastic origin. These two cell-masses 

 are again met with in the larva, only slightly altered 

 in form ; they lie near together, a little above the anus ; 

 they are composed of very small cells with clear 

 nuclei; they stain more deeply than the surrounding 

 tissues. There is not any distinction between the 

 peripheral and central cells. 



During the larval stage the cell-masses increase in 

 size by addition to the number of cells. Their diameter 

 immediately before the first ecdysis is about 9 p. At 

 the same time that the imaginal discs of the fourth 

 pair of legs appear these generative glands become 

 coated with a soft membrane, which ends in a short 

 tube ; by these tubes, which must be regarded as the 

 commencement of ducts, the generative glands are 

 attached to the anterior end of the anal slit, so that 

 they have the appearance of being produced by 

 imagination of the wall of the rectum. 



* Nalepa, Anat.,' p. 137. 



